On Tue, May 6, 2008 at 4:14 PM, Michael Goffioul
<[EMAIL PROTECTED]> wrote:
> On Tue, May 6, 2008 at 6:33 PM, Xavier Delacour
>
> <[EMAIL PROTECTED]> wrote:
>
> > buf[sz] like this shouldn't dereference buf[sz].
>
> I'm not following this sentence....
Sorry. I meant to say that buf[sz] should return a reference to
start_of_array + sz, but not actually read the memory at that
location.
>
>
> > Maybe it's a
> > difference between MS and gcc STL implementations (though I thought it
> > was standard.. do you have a segfault at this point?). buf[sz] ought
> > to return a reference, &buf[sz] converts it to a pointer.
>
> Indeed, I get a segfault at this point. When debugging, I see that
> vector<T>::operator[] is really executed with an out-of-bound index.
> And this really dereference and invalid memory location. If you look
> into MSVC header you find something like:
>
> reference operator[](size_type _Pos)
> { // subscript mutable sequence
> return (*(_Myfirst + _Pos));
> }
Huh. Well, I wouldn't expect this to "dereference" (_Myfirst + _Pos),
by which I mean "read the byte from memory" any more than I would
expect
char* p = (char*) 0;
char& r = *p;
to crash (it doesn't, under gcc). Flipping through the standard for a
few minutes doesn't yield a clear answer, however the resident
language lawyer here suspects it isn't defined one way or the other..
along with my original usage of std::vector.
Anyway, I think the following form is the proper one,
std::copy(buf.begin(), buf.begin()+sz, (char*)ptr);
I'll update accordingly once I receive a patch from someone with the
various Windows related fixes (even if partial).
Thanks,
Xavier
>
> Michael.
>
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